α galactosylceramide, compound A, and its derivatives, have been known as biologically active agents for some time. See, e.g., U.S. Pat. No. 5,936,076 to Higa, et al., and U.S. Pat. No. 6,531,453 to Taniguchi, et al., describing several derivatives as anti-tumor agents as well as immunostimulators, both of these being incorporated by reference in their entirety.

The base compound, i.e., α-galactosylceramide or “αGal-Cer” hereafter is described by Nattori, et al., Tetrahedron, 50:2271 (1994), incorporated by reference, has itself been shown to inhibit tumor growth. See, Koejuka, et al., Recent Res. Cancer, 1:341 (1999). Sharif, et al., Nature Med., 7:1057 (2001), and Hong, et al., Nature Med., 7:1052 (2002), show efficacy against type I diabetes.
Study of the structure of αGal-Cer shows that it contains a sphingosine chain. Truncation of this chain has been shown, by Miyamoto, et al., Nature, 413:531 (2001), to result in a compound preventing autoimmune encephalomyelitis.
In parallel work it has been shown that natural killer T cells (NKT cells) recognize lipid antigens that are presented by the major histocompatibility complex-class I like protein, CD1d, for example. See, Godfrey et al., J. Clin. Invest., 114:1379-1388 (2004).
Singh, et al., J. Immunol., 163:2373 (1999), and Burdin, et al., Eur. J. Immunol., 29:2014 (1999), have shown that αGal-Cer and CD1d potentiate Th2-mediated, adaptive immune responses, via activation of Vα14 natural killer T (NKT) cells.
The proposed mechanism by which αGal-Cer prevents disease is its ability to suppress interferon-gamma, but not interleukin-4, by NKT cells. See, e.g., Brossay, et al., J. Exp. Med., 188:1521 (1998); Spada, et al., J. Exp. Med., 188:1529 (1998), who showed the recognition of αGal-Cer by NKT cells, suggesting therapeutic efficacy in humans.
αGal-Cer has been developed as a potential therapeutic compound and taken into clinical testing, see, for example, Giaccone et al., Clin Canc. Res., 8, 3702-3709 (2002). However, following treatment with αGal-Cer, the level of NKT cells in the peripheral blood of treated cancer patients treated fell to undetectable levels within 24 hours of treatment and failed to regain pretreatment levels within the remaining time course of the study.
Loss of circulating levels of NKT cells could represent a significant limitation therapeutically as it could suggest that therapeutic stimulation of NKT cells could not be used as a repeated treatment.
There is thus an interest in synthesis of analogues of αGal-Cer which act as stimulators of NKT cells but which do not lead to rapid loss of circulating levels of NKT cell populations after therapeutic administration.
Various publications describe synthesis of αGal-Cer and its derivatives. An exemplary, but by no means exhaustive list of such references includes Morita, et al., J. Med. Chem., 38:2176 (1995); Sakai, et al., J. Med. Chem., 38:1836 (1995); Morita, et al., Bioorg. Med. Chem. Lett., 5:699 (1995); Takakawa, et al., Tetrahedron, 54:3150 (1998); Sakai, et al., Org. Lett., 1:359 (1998); Figueroa-Perez, et al., Carbohydr. Res., 328:95 (2000); Plettenburg, et al., J. Org. Chem., 67:4559 (2002); Yang, et al., Angew. Chem., 116:3906 (2004); Yang, et al., Angew. Chem. Int. Ed., 43:3818 (2004); and, Yu, et al., Proc. Natl. Acad. Sci. USA, 102(9):3383-3388 (2005).
Studies have been conducted to examine the biological impact of the αGal-Cer molecule, when modifications of its structure were made. Higa, et al., supra, as well as, Zhou, et al., Org. Lett., 4:1267 (2002); Schmieg, et al., J. Exp. Med., 198:1631 (2003), Barbieri, et al., J. Org. Chem., 468 (2004); and Fan, et al., Tetrahedron, 61:1855 (2005), are examples of the limited literature on this topic. Tsuji, et al., J. Exp. Med., 198:1631 (2003), prepared a synthetic, C-glycoside analogue, i.e., α-C-Gal-Cer, which acts on NKT cells, in vivo, stimulating enhanced, Th1-type immune responses in mice. The protection against microbial infection and anti-tumor efficacy (Sköld, et al., Infect. Immun., 71:5447 (2003); Sharif, et al., supra; Hong, et al., supra) are of special interest.
Additional work on the mechanism of action of these compounds is shown by, for example, Parekh, et al., J. Immunol., 173:3693-3706 (2004), and Brossay, et al., supra.
Examples of US Patents and Patent Applications or International Patent Applications describing instances of such derivatives and or the biological activity of αGal-Cer analogs include U.S. Pat. No. 5,936,076 to Higa, et al., and U.S. Pat. No. 6,531,453 to Taniguchi, et al., U.S. Pat. No. 5,853,737 to Modlin et al., US Patent Application 2003030611 to Jiang et al., US Patent Application 20030157135 to Tsuiji et al., US Patent Application 20040242499 to Uernatsu et al and International Patent Applications describing No. PCT/JP20021008280 to Yamamura at al.
Essentially all of these prior examples describe analog structures based on αGal-Cer. Identification and characterization of molecules which are not glycolipids, such as αGal-Cer and its analogs, has been limited. Examples of Patent Applications describing structures which do not appear to be analogous to αGal-Cer include acyl peptides of US Patent Application No. 20040265976 to Moody et al., and JP Patent Application 34540997 to Masunaga et al.
We have now found a novel group of compounds that substantially mimic the binding properties of α-GalCer with the human CD1d molecule, but differs significantly in the interaction with T-cell receptors (TCR), leading to unexpected and advantageous properties compared to α-GalCer.